The demands on automobiles for better fuel economy have been increasing in recent years as concern with environmental issues has been rising. Good fuel economy is also being required of the rubber compositions used for automotive tires. For example, rubber compositions containing a conjugated diene polymer (e.g., polybutadiene, butadiene-styrene copolymer) and a filler (e.g., carbon black, silica) are used for the rubber compositions for automotive tires.
For enhancing fuel economy, a method is known which includes reducing the amount of a filler to suppress heat build-up of rubber compositions. However, the reduction in the amount of a filler decreases the hardness of the rubber compositions, which may deteriorate the handling stability, and also may deteriorate the abrasion resistance and wet-grip performance. Thus, a method is demanded which enhances the fuel economy, wet-grip performance, abrasion resistance, and handling stability in a balanced manner.
Patent Literature 1 teaches that fuel economy can be enhanced by mixing a diene rubber which is modified by an organic silicon compound containing an amino group and an alkoxy group. Patent Literature 2 teaches that wet-grip performance can be improved by using both of anhydrous silica and hydrous silica. However, those techniques need to be improved in terms of enhancing fuel economy, wet-grip performance, abrasion resistance, and handling stability in a balanced manner.